Japan, South Korea and the United States held an unprecedented trilateral missile defense exercise Tuesday, aimed at countering the growing threat from nuclear-armed North Korea, which denounced it as a “military provocation.”

The drill in waters off Hawaii came less than a week after North Korea flight-tested a powerful new medium-range ballistic missile that leader Kim Jong Un hailed as a strike threat to U.S. military bases across the Pacific.

The trilateral exercise included a ballistic target tracking operation to test the Aegis anti-missile systems used by the U.S. and its two key Asian allies.